Various fluids are transported by railway tank cars. Such tank cars have domes where various valves are located. The portions of the valves that are external to the tank, including the valve handles are housed within a protective housing that has a hinged lid or cover that is opened to expose the handles. One or more of the valves is opened during certain procedures involving loading and/or unloading fluid into and/or from the tank. During such procedures, a valve closure assembly having a power actuator is hoisted onto the dome and mounted there. The power actuator is fitted to the handle of the open valve and can be remotely and automatically operated to close the open valve when conditions call for valve closing.